A suppressor or a sound suppressor is a device that may be attached to the barrel of a firearm which reduces the amount of noise and visible muzzle flash generated when firing. While suppressors are desirable for stealth purposes, they are also desirable for mitigating noise pollution and lowering the risks of hearing loss.
Suppressors are typically constructed of a metal cylinder body with internal mechanisms that reduce the sound of firing by slowing the escaping propellant gas. The most common internal mechanisms are baffles. Baffles are typically circular metal dividers which separate the cylinder body into expansion chambers. A suppressor typically has multiple baffles. Each baffle has a hole in its center to permit the passage of the bullet. The hole is usually slightly larger than the bullet caliber to minimize the risk of the bullet hitting the baffle. Spacers typically separate the baffles and keep them aligned at a specified distance from each other inside the suppressor.
Suppressors are regulated by firearm legislation in most countries. While some countries allow civilian use of suppressors, other governments have opted to ban them from civilian use. In the United States, possession of suppressors is legal in most states, but regulations make purchasing them difficult. Regulations for making one's own suppressor are easier to comply with, and many people do make their own. The baffles are the key parts of the suppressor and individual baffles are treated as suppressors themselves. Hence one cannot buy suppressor baffles ready to be assembled into a suppressor or contract out the work of making them with any less regulatory difficulty than purchasing an entire suppressor.
Many designs for making a suppressor are available and if one has access to a fully equipped machine shop, particularly lathe tools, making one's own suppressor is not too difficult. However, many people do not have easy access to a fully equipped machine shop. Some suppressor designs are devised for people who have access to a limited set of tools.
Some popular suppressor designs that require minimal tools modify engine block freeze plugs to make the baffles. Engine block freeze plugs (or core plugs) are thin metal cups (see FIGS. 2a and 2b) used to plug holes left in the engine blocks of water-cooled internal combustion engines as part of the manufacturing process. Holes are put into the casting of an engine block to support internal sand forms, and to facilitate the removal of the sand after the casting has cooled. It is also thought that core plugs will pop out and protect the engine block from cracking in the event that the coolant water in the engine block freezes and expands. Hence core plugs are popularly called frost plugs, freeze plugs, or engine block expansion plugs. Freeze plugs are inexpensive, readily available through auto parts stores, and are not subject to firearms regulations.
To make baffles for a suppressor, freeze plugs are typically reformed from a cup that is “U” shaped in cross-section to a cup that has a conical depression in the middle with an “M” shaped cross-section. In some design methods, the conical depression is formed by drilling a hole in the center of the unmodified freeze plug, then putting it into a vise along with an object, such as a ball bearing, that has an increasing cross-section diameter that ultimately is somewhat larger in cross-section diameter than the center hole. The vise is then tightened and the freeze plug reformed into an “M” baffle. A socket from a wrench set can be used to hold the freeze plug during the compression in the vise. However, this method is not all that reliable. The center hole expands about 50% during the process, with a good deal of variation between each baffle made this way. It is highly desirable to have the center hole only slightly larger than the bullet. So this means that the finished baffles must be measured to ensure desired tolerances for the size of the center hole are met. Typically many do not and must be discarded. Alternatively, one can undersize the initial drilling of the center hole, then re-drill the center hole after the vise reforming. However, this is hard to do without a drill press using only a hand-held drill and still keep the center of the center hole in the center of the baffle. The finished baffles must be measured to ensure desired tolerances for the location of the center hole are met. Again, many typically will not and must be discarded.
What is needed is a simple and reliable method for making baffles from engine block freeze plugs using only simple hand tools and not high precision machine shop tools.